1. Field of the Invention
The present invention relates to an improver of a ratio of a polishing rate of an insulating film to that of a stopper film. Further, the present invention relates to a polishing composition comprising the improver, a process for selectively increasing a ratio of a polishing rate of an insulating film to that of a stopper film using the improver, and a process for producing a substrate to be polished using the above-mentioned polishing composition.
2. Discussion of the Related Art
Conventionally, an isolation region has been formed by a so-called LOCOS (Local Oxidation of Silicon) method. However, the LOCOS method does not meet the requirement for high-integration of semiconductors in recent years because the isolation region has become too narrow for the LOCOS method. Therefore, recently, there has been employed a so-called STI (Shallow Trench Isolation) method comprising depositing a stopper film such as a silicon nitride film on a silicon substrate, embedding an insulating film such as a silicon oxide film in a trench part, planing an excessive insulating film in the external part of the trench by using chemical-mechanical polishing (CMP) to expose the stopper film, and thereafter removing the stopper film by etching. In the STI method, it is desired that a ratio of the polishing rate of the insulating film to that of the stopper film is increased in order to prevent dishing or thinning generated during polishing of the insulating film on a substrate to be polished, thereby achieving planarization of the insulating film.
Presently, a ceria polishing agent used as a polishing agent for STI-CMP exhibits a high polishing rate of an insulating film, and selectively controls a polishing rate of a stopper film, thereby achieving efficient planarization. However, as compared to a silica polishing agent, there arise some problems such that the ceria polishing agent is high in costs, and abrasive grains are not easily dispersed therein. On the other hand, a commercially available polishing agent has a low ratio of a polishing rate of an insulating film to that of a stopper film. Therefore, there arise a problem such that polishing is undesirably progressed at parts where trench portions are closely arranged, as compared to parts where there are fewer trench portions, so that thinning is likely to be generated. In addition, when a stopper film is made thicker in order to prevent thinning, there arise a problem such that an insulating film in the trench part remains in a large amount by removal of the stopper film after CMP, so that there is still yet a great difference in the levels (step height) between a silicon substrate surface and an insulating film surface.
There have been reported that a ratio of polishing rates can be increased by adding triethanolamine as disclosed in Japanese Patent Laid-Open No. Hei 11-330025, or adding tetramethylammonium hydroxide and hydrogen peroxide as disclosed in Japanese Patent Laid-Open No. Hei 10-270401. However, in the former method, there arise some problems such that addition of a large amount of triethanolamine so as to have a concentration of 10% by weight or more is needed in order to exhibit its effects, thereby increasing its costs including costs for waste water treatment. In the latter method, hydrogen peroxide is likely to be decomposed, so that its effects, including stability, are not sufficient.
An object of the present invention is to provide an improver of a ratio of a polishing rate of an insulating film to that of a stopper film for stably and selectively increasing the ratio of a polishing rate of an insulating film to that of a stopper film.
Another object of the present invention is to provide a polishing composition comprising the improver, a process for selectively increasing a ratio of a polishing rate of an insulating film to that of a stopper film, and a process for producing a substrate to be polished using the above-mentioned polishing composition.
These and other objects of the present invention will be apparent from the following description.